362 BACTERIOLOGY. 



pearance of alternate stained and colorless portions. 

 The latter portions are believed to be the spores of 

 the organism, though as yet no incontestable proof of 

 this opinion has been presented. At times these colorless 

 portions are seen to bulge slightly beyond the contour 

 of the rod, and in this way give to the rods the beaded 

 appearance so commonly ascribed to them. 



STAINING-PECULIARITIES. A peculiarity of this 

 organism is its behavior toward staining-reagents, and 

 by this means alone it may be easily recognized. The 

 tubercle bacillus does not stain by the ordinary methods. 

 It possesses some peculiarity in its composition that 

 renders it proof against the simpler staining processes. 

 It is therefore necessary that more energetic and pene- 

 trating reagents than the ordinary watery solutions 

 should be employed. Experience has taught us that 

 certain substances not only increase the solubility of the 

 aniline dyes, but by their presence the penetration of 

 the coloring-agents is very much increased. Two of 

 these are aniline oil and carbolic acid. They are 

 employed in the solutions to about the point of satura- 

 tion. (For the exact proportions, see chapter on Stain- 

 ing-reagents.) 



Under the influence of heat these solutions are seen 

 to stain all bacteria very intensely the tubercle bacilli 

 as well as other forms. If we subject our prepara- 

 tion, which may contain a mixture of tubercle bacilli 

 and other species, to the action of decolorizing-agents, 

 another peculiarity of the tubercle bacillus will be 

 observed. While all other organisms in the prepara- 

 tion give up their color and become invisible, the 

 tubercle bacillus retains it with marked tenacity. It 

 stains with great difficulty ; but once stained it retains 



